Sporting CP are prepared to sell Matheus Nunes this month.
Correio de Manha says Sporting are braced for bids in the final weeks of the window.
Everton are named as the frontrunners for Nunes' signature with £17.1m enough to do the deal.
Nunes, 22, cost just £425,000 when Lisbon snapped him up from Estoril in 2019 and he has turned into an integral part of their league-winning side.
The Brazilian midfielder made 39 appearances last year as the capital club claimed their first Primeira Liga title in 19 years, and he also played a part in last month's Supercup victory over Braga.